Thermal management of RF devices using embedded microjet arrays

ABSTRACT

The present invention generally relates to a microjet array for use as a thermal management system for a heat generating device, such as an RF device. The microjet array is formed in a jet plate, which is attached directly to the substrate containing the heat generating device. Additional enhancing features are used to further improve the heat transfer coefficient above that inherently achieved by the array. Some of these enhancements may also have other functions, such as adding mechanical structure, electrical connectivity or pathways for waveguides. This technology enables higher duty cycles, higher power levels, increased component lifetime, and/or improved SWaP for RF devices operating in airborne, naval (surface and undersea), ground, and space environments. This technology serves as a replacement for existing RF device thermal management solutions, such as high-SWaP finned heat sinks and cold plates.

This application is a Continuation of U.S. patent application Ser. No.16/712,316 filed Dec. 12, 2019, which is a Continuation of U.S. patentapplication Ser. No. 15/797,784 filed Oct. 30, 2017 (now U.S. Pat. No.10,651,112 issued May 12, 2020), which claims priority to U.S.Provisional Application Ser. No. 62/415,704, filed Nov. 1, 2016 and U.S.Provisional Application Ser. No. 62/415,739, filed Nov. 1, 2016, thedisclosures of which are incorporated by reference in their entireties.

This invention was made with Government support under Contract No.FA8721-05-C-0002 awarded by the U.S. Air Force. The Government hascertain rights in the invention.

BACKGROUND OF THE INVENTION

Many electronic components, such as processing units, and radiofrequency (RF) devices, are commonly used in many of today's circuitsand generate significant amounts of heat. For example, RF devices, suchas high electron mobility transistors (HEMTs), are commonly used inradar (aircraft surveillance, weather surveillance, tactical);electronic warfare (EW), including jamming; RF communication systems;and other applications. Processing units, such as CPUs, are commonlyused in computers, laptops, mobile electronics, and other applications.

A limiting factor in many of these applications is the maximum componenttemperature of the heat generating device, which may occur, for example,within the gate region of a HEMT. Component lifetime is a function ofmaximum temperature, and as such, a trade-off is often made betweenlifetime, maximum power output, and/or duty cycle.

The maximum component temperature in these heat generating devices isgoverned by heat transfer at several layers.

First, the conductive thermal resistance through the heat generatingcomponent itself is a factor in determining the maximum componenttemperature. The electrically active region of a heat generating deviceis typically located on one side of a semiconductor substrate, which maybe, for example, silicon, gallium nitride, or gallium arsenide. This isthe region where waste heat is generated. This heat must be conductedthrough the substrate before being dissipated through the thermalmanagement system. Thermal resistance scales with thickness.

Second, the heat transfer from the surface of the semiconductorsubstrate to the thermal management system is a factor in determiningthe maximum component temperature. Thermal management systems usuallyconduct heat from the heat generating device into a spreader or heatsink. These systems then dissipate the heat to the ambient environment,such as via free convection, conduction, or radiation, or to a coolant,using forced convection.

Existing technologies use finned heat sinks, cold plates, microchannels,or radiators for this purpose. Thus, the heat transfer from the heatgenerating device can be limited by the performance of thesetechnologies. For example, these technologies usually rely on thepresence of a thermal interface material (TIM) between the component andthe thermal management system. The thermal interface material, even ifchosen to have low resistance, still reduces the efficiency of anysolution.

Further, the size, weight, and power (SWaP) of existing thermalmanagement solutions often drives the design of these systems and canlimit their performance. For example, the system in which the heatgenerating device is contained may be compact, limiting the ability totransfer the heat to a cooler ambient location.

Therefore, it would be beneficial if there were a thermal managementsystem that addressed these challenges by minimizing the conductive andconvective thermal resistance in heat generating devices and reducing oreliminating the dependence on SWaP-constraining heat sinks, spreaders,and similar devices.

SUMMARY OF THE INVENTION

The present invention generally relates to a microjet array for use as athermal management system for a heat generating device, such as an RFdevice. The microjet array is formed in a jet plate, which is attacheddirectly to the substrate containing the heat generating device.Additional enhancing features are used to further improve the heattransfer coefficient above that inherently achieved by the array. Someof these enhancements may also have other functions, such as addingmechanical structure, electrical connectivity or pathways forwaveguides. This technology enables higher duty cycles, higher powerlevels, increased component lifetime, and/or improved SWaP for RFdevices operating in airborne, naval (surface and undersea), ground, andspace environments. This technology serves as a replacement for existingRF device thermal management solutions, such as high-SWaP finned heatsinks and cold plates.

In one embodiment, an assembly is disclosed. The assembly comprises asemiconductor component, having a heat generating device disposedtherein; and a jet plate, directly bonded to an impingement surface ofthe semiconductor component, where a reservoir is formed within theassembly between the jet plate and the semiconductor component, whereinthe jet plate comprising a microjet and an exhaust port in communicationwith the reservoir. In certain embodiments, a single-phase fluid isdisposed in the reservoir. In certain embodiments, the jet platecomprises a plurality of microjets arranged as an array. In someembodiments, the impingement surface is a side opposite a side where theheat generating device is disposed. In other embodiments, theimpingement surface is a side where the heat generating device isdisposed. In certain embodiments, the jet plate comprises a wall jetfeature disposed in the reservoir. In some embodiments, the wall jetfeature extends from the jet plate to the impingement surface. In otherembodiments, the wall jet feature extends upward from the impingementsurface into the reservoir. In some embodiments, a channel is disposedwithin the wall jet feature. That channel may comprise an electricalconduit or a pathway allowing light and electromagnetic waves to passtherethrough. In certain embodiments, the assembly further comprises aneffluent control feature, which extends from the jet plate to theimpingement surface and directs flow of effluent toward the exhaustport. In certain embodiments, a channel may be disposed in the effluentcontrol feature. That channel may comprise an electrical conduit or apathway allowing light and electromagnetic waves to pass therethrough.

According to another embodiment, a method of cooling a semiconductorcomponent is disclosed. The method comprises directing a single-phasecoolant fluid through a plurality of microjets toward a surface of thesemiconductor component such that the single-phase coolant fluid strikesan impingement surface; and exhausting the single-phase coolant fluidthrough an exhaust port away from the semiconductor component after thesingle-phase coolant fluid strikes the impingement surface. In certainembodiments, the method further comprises controlling the flow ofeffluent toward the exhaust port. In some embodiments, the effluent isrouted so as to avoid an impingement surface of an adjacent microjet. Incertain embodiments, the heat transfer properties are improved. Incertain embodiment, the surface area of the impingement surface isincreased to increase contact between the semiconductor component andthe single-phase coolant fluid. In certain embodiments, wall jetfeatures that extend perpendicular to the impingement surface areprovided to increase single-phase heat transfer by boundary layersuppression and also increase contact area.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the present disclosure, reference is madeto the accompanying drawings, in which like elements are referenced withlike numerals, and in which:

FIG. 1 is an illustration of the top surface of a substrate containing aheat generating device.

FIG. 2 is an illustration of the top surface of the jet plate that bondsto the bottom surface of the substrate.

FIG. 3 is an illustration showing the jet plate bonded to the substrate.

FIG. 4 shows the fluid streamlines predicted analytically for the arrayof microjets shown in FIG. 2.

FIG. 5 shows the heat transfer coefficient on the impingement surface.

FIG. 6A-6F show the jet plate during various stages of fabricationaccording to one embodiment.

FIG. 7 shows a flowchart detailing the fabrication process of FIGS.6A-6F.

FIG. 8A-8B show the fabrication of the assembly according to anotherembodiment.

FIG. 9 shows the fluid flow through a microjet.

FIG. 10 shows area enhancement structures located in the impingementzone.

FIG. 11 shows primary and secondary stagnation points in a microjetarray.

FIG. 12 shows an example of wall jet features.

FIG. 13 shows a perspective view of the impingement surface with walljet features.

FIG. 14 shows an example of effluent flow control features.

FIG. 15 shows a top view of full height features having additionalfunctions.

FIG. 16 shows a perspective view of the full height features havingadditional functions.

DETAILED DESCRIPTION

Microjet impingement is a heat transfer technique by which a jet or anarray of jets impinge onto a surface for the purpose of transferringheat between the surface and the fluid of the jet. Jets can be formed bythe use of nozzles, tubes or an orifice plate and are characterized byhaving a substantially higher momentum in one direction than thesurrounding fluid. Typically, a turbulent jet exit velocity profile isflat across the radius, reducing to zero at the edge due to the presenceof the nozzle. This high velocity jet suppresses the thermal boundarylayer at the heat transfer surface resulting in high heat transfercoefficients.

Adjacent fluid, particularly if it is the same fluid, is entrained intothe core of the jet, spreading the momentum of the jet out to a largerand larger radius as the jet propagates downstream. At the point wherethe centerline of the jet meets the impingement surface, a stagnationpoint exists due to symmetry. Near this point, the flow turns from thedirection of jet travel to parallel the impingement surface. Theresulting flow is often referred to as a wall jet.

Microjets and microjet arrays can also provide higher heat transfercoefficients than other single or multi-phase technologies, whileeliminating the need for any low conductance thermal interfacematerials, which degrade overall thermal performance.

Additionally, microjet arrays can be located closer to the electricallyactive region of the device than other thermal management systems and,in many cases, may be integrated into the fabrication process of thedevices.

For particularly sensitive circuitry, single-phase microjets also offera continuous phase. This may help to minimize possible transient effectson nearby circuits from sharp discontinuities in permittivity. Singlephase systems also lessen the density difference between microjets andsurrounding fluid, making them more robust against changes inorientation or incident inertial accelerations than two-phase (e.g.,boiling) systems.

FIG. 1 shows a top surface of a component 100 having a heat generatingdevice 110. The component 100 may be formed on or in a substrate, suchas silicon, gallium nitride, gallium arsenide or others. The heatgenerating device 110 may comprise one or more electronic circuits, suchas transistors, FETs, and other semiconductor functions. The component100 is typically a semiconductor component, which includes at least oneelectronic function or circuit. The component 100 is typically formedsuch that the electronics, including the heat generating device 110, areexposed on one surface and not exposed on the opposite surface. Forexample, semiconductors are typically fabricated by etching, depositingand doping one side of the substrate. Throughout this disclosure, thesurface where the heat generating device is exposed is referred to asthe active surface 101 of the component 100. The opposite surface of thecomponent 100 is referred to as the impingement surface 102. The activesurface 101 of the component 100 may also include other features, suchas contact pads 120.

FIG. 2 shows a top view of the jet plate 200. The jet plate 200 may beformed from a single substrate, which may be processed in accordancewith traditional semiconductor fabrication processes. The top surface201 of the jet plate 200 is bonded to the impingement surface 102 of thecomponent 100 when assembled. The jet plate 200 has a reservoir 210disposed on the top surface 201. This reservoir 210 defines the volumein which the coolant is disposed. The reservoir 210 may be any suitableshape, including circular, square, or irregularly shaped, as shown inFIG. 2. In certain embodiments, the jet plate 200 may have a thicknessof about 450 μm, while the reservoir 210 has a depth of about 200 μm. Ofcourse, other dimensions may be used, as long as the thickness of thejet plate 200 is sufficient relative to the depth of the reservoir 210so as to be structurally sound and integral. In certain embodiments, thereservoir may have a top-view area of approximately 3.5 mm×3.5 mm. Ofcourse, other dimensions may be used, as long as the reservoir area islarge enough to include both the microjet or microjet array as well asthe exhaust ports.

The reservoir 210 has various openings. There are one or more microjets220 in communication with the reservoir 210. In certain embodiments,only one microjet 220 may be employed. In other embodiments, such asthat shown in FIG. 2, an array of microjets 220 may be used. Forexample, as noted above, an array of microjets 220 may be used. Thisarray may be square, such as 4×4, 5×5 or 6×6. In other embodiments, thearray may be rectangular, such as 3×4 or 4×5. In yet other embodiments,the microjets 220 may be arranged in a plurality of concentric circles.The arrangement of the microjets 220 is not limited by this disclosure.

One or more exhaust ports 230 are also in communication with thereservoir 210. In certain embodiments, these exhaust ports 230 may belocated outside of the microjets 220. In other words, the microjets 220may be arranged in a particular configuration. The smallest perimeterthat surrounds these microjets 220 does not include the exhaust ports230. FIG. 2 shows the microjets 220 arranged as a square array, whilethe exhaust ports 230 are clearly outside the perimeter that definesthat square. In other embodiments, the exhaust ports 230 may be disposedwithin the perimeter that surrounds the microjets 220.

In certain embodiments, the microjets 220 may each have a diameter inthe range of 100 to 150 μm, while the exhaust ports 230 have a diameterin the range of 1 to 2 mm. Of course, other dimensions may also be used.

The microjets 220 serve as the ingress for the coolant, while theexhaust ports 230 serve as the egress.

Although not visible, the bottom surface 202 of the jet plate 200 may beplanar.

FIG. 3 shows the assembly created by bonding the top surface 201 of thejet plate 200 to the impingement surface 102 of the component 100. Thereservoir 210 becomes a sealed enclosure when bounded at the open topside by the impingement surface 102 of the component 100. Whenassembled, the only openings in communication with the reservoir 210 arethe microjets 220 and the exhaust ports 230.

The microjets 220 are aimed at the impingement surface 102, wherelocally high fluid velocities, boundary layer suppression, and turbulentmixing produce extremely high convective heat transfer coefficientsbetween the impingement surface 102 and the coolant. Microjets 220 canbe arrayed geometrically to cool larger surface areas, with heattransfer coefficients from a single-phase system of greater than 400kW/m²K averaged over a 1 mm² impingement surface, as indicated bycomputational fluid dynamics analyses of typical geometries. This mayprovide significant advantages over current advanced cold plate designshaving performance on the order of 1 kW/m²K, and even multi-phasemicrochannel approaches on the order of 10 s of kW/m²K.

The microjet 220 and the reservoir 210 are designed to be utilized withsingle-phase coolant fluid. In other words, the coolant fluid in thedevice does not change phase (for example, boil) within the device. Thefluid microjets 220 are therefore submerged or surrounded by thereservoir 210 of the same fluid. Fluid enters the microjets 220 towardthe impingement surface 102. The fluid is confined by the reservoir 210and eventually exits through the exhaust ports 230 in the same state ofmatter as it entered. This eliminates any considerations related tocritical heat flux (CHF) and avoids the need for complex wettingstrategies, like wettability coatings, both of which must often beaddressed with multi-phase systems.

The reservoir 210 is preferably positioned so as to be verticallyaligned with the heat generating device 110. In this way, coolant isdirected toward the impingement surface 102 directly beneath the heatgenerating device 110.

A gasket 250 may be disposed on the bottom surface 202 of the jet plate200 so as create a liquid-tight seal around the microjets 220. Othermeans of creating a liquid-tight seal may also be used.

In operation, a pressurized coolant is in communication with themicrojets 220 on the bottom surface of the jet plate 200. This coolantmay be any suitable fluid, including air, water, ethylene glycol,propylene glycol, ethanol, R134A, ammonia, or a combination of two ormore of these fluids. In other embodiments, other fluids may be used asthe coolant. The coolant is pressurized to a pressure of about 10 psi.In certain embodiments, the pressure of the coolant may be as high as 30psi, although other pressures may be used. The coolant may flow througha manifold (not shown) to an opening that is surrounded by gasket 250.

This pressurized coolant flows through the microjets 220 and strikes theimpingement surface 102 of the component 100. The coolant may exit themicrojets 220 at velocities of between 10 and 30 m/s, although othervelocities may be achieved by adjusting the pressure of the coolant, orthe geometry of the microjet or microjet array. Heat is transferred tothe coolant in this process. The heated coolant then exits the reservoir210 through the exhaust ports 230. The heated coolant may then be cooledexternally, using a heat exchanger, or other known techniques. As statedabove, the heat transfer is a single phase action, where the state ofthe coolant is not changed due to heat transfer. For example, thecoolant may remain a liquid throughout the heat transfer process.

FIG. 4 shows fluid streamlines, as predicted analytically usingcomputational fluid dynamics. These streamlines impinge upon theimpingement surface 102 of the component 100. The coolant is heated andits velocity is turned and decreases. In this figure, the coolant exitsthrough exhaust ports located outside of the array of microjets 220.Higher velocity streams are shown in dotted lines, while lower velocitystreams are shown in solid lines.

FIG. 5 shows the heat transfer coefficient on the impingement surface102. In this figure, the microjets 220 are arranged as a 4×4 arrayspread over an area of 1 mm². Each microjet 220 has a diameter of 100μm. In this example, the mean microjet velocity is 30 m/s. The heattransfer coefficient is as high as 600,000 W/m²K. This heat transfercoefficient decreases moving away from the impingement zone.

Importantly, the jet plate 200 may be integrated directly with thecomponent 100. Further, the jet plate 200 may be fabricated using thesame semiconductor processes used to create the component 100.

FIG. 6A-6F shows the fabrication process according to one embodiment.FIG. 7 is a flowchart illustrating this process.

In FIG. 6A, a substrate 400 is shown. The substrate 400 may be a siliconsubstrate, for example. The substrate 400 has a top surface 401 and abottom surface 402. The substrate 400 may first by thinned to thedesired thickness. This thickness may be, for example, about 500 μm,although other thicknesses may be used. In certain embodiments, a CMP(Chemical Mechanical Planarization) process is performed. In someembodiments, the top surface 401 of the substrate 400 may be planarizedto within less 10 angstroms of planar. This is also shown in Process 500of FIG. 7.

After thinning, the substrate 400 may be etched so as to create areservoir 210, as shown in FIG. 6B and in Process 510 of FIG. 7. Thisetch process may be performed by disposing a mask, such as aphotoresist, on a portion of the top surface 401 of the substrate 400.The etch process may be a wet etch process or a dry etch process. Incertain embodiments, about 200 μm of material are etched from the topsurface 401 to form the reservoir 210.

After the reservoir 210 has been formed, a protective film 403 may beapplied to the top surface 401 of the substrate to protect the topsurface 401 from further processing, as shown in FIG. 6C and Process 520of FIG. 7. In certain embodiments, this protective film 403 may be asilicon nitride layer.

The microjets 220 and exhaust ports 230 are then etched in the substrate400, preferably from the bottom surface 402, as shown in FIG. 6D andProcess 530 of FIG. 7. This may be performed in a similar manner as thereservoir 210. In other words, this etch may be performed by disposing amask 404, such as a photoresist, on a portion of the bottom surface 402of the substrate 400. The mask is patterned to expose the exhaust ports230 and the microjets 220. The etch process may be a wet etch process ora dry etch process.

Once all of the etching has been completed, the protective film 403 isremoved from the top surface, as shown in FIG. 6E and Process 540 ofFIG. 7. This completes the processing of the substrate 400, as thesubstrate 400 has now been transformed into the jet plate 200. The jetplate 200 is now ready to be bonded to the component 100.

In certain embodiments, the impingement surface 102 of the component 100is planarized, such that its smoothness is within less than 10angstroms.

In one embodiment, the jet plate 200 is bonded to the impingementsurface 102 of the component 100 simply by pressing the jet plate 200against the component 100. If the two surfaces (the impingement surface102 and the top surface 201) are sufficiently smooth, such as less than10 angstroms in certain embodiments, the two parts will adhere to oneanother via van der Waal's forces. This may be referred to as silicondirect bonding, or silicon fusion bonding. In some embodiments, thecomponent 100 and the jet plate 200 may be heated prior to the bondingprocess, or bonded by other methods including eutectic gold bonds,indium solders, or other adhesives. In certain embodiments, prior to thebonding process, the parts, which may be silicon, may be exposed tooxygen or the ambient environment, so as to create a thin film ofsilicon oxide on the outer surfaces. In other certain embodiments, aconductive ground plane may be included between the jet plate and theimpingement surface. Of course, other techniques may be used to create asilicon oxide film on the surfaces of the component 100 and the jetplate 200. The assembly after the bonding process is completed is shownin FIG. 6F and Process 550 of FIG. 7.

Variations of the process shown in FIGS. 6A-6F and FIG. 7 are alsopossible. For example, it is possible to etch the microjets 220 andexhaust ports 230 prior to creating the reservoir 210. In other words,processes 510 and 530 may be performed in the opposite order. In thisvariation, it may be beneficial to apply a mask or protective film tothe top surface 401 of the substrate 400 prior to etching the microjets220 and exhaust ports 230 to minimize damage done to the top surface401.

In certain embodiments, it may be advantageous to perform an alignmentprocess to align the jet plate 200 to the component 100 prior tobonding. This may be performed in several ways.

In one embodiment, a metal alignment key is provided in a location inthe impingement surface 102 and in a corresponding location in the topsurface 201 of the jet plate 200. To minimize disruption to the bondingprocess, these metal alignment keys may be depressed into theserespective surfaces. For example, a small region of the impingementsurface 102 may be etched to create a recess. A metal may be depositedin this recess. A similar process may be performed to the top surface401 of the substrate 400. In certain embodiments, these metal alignmentkeys are complementary shapes, such that the component and jet plate arealigned when the shapes fit together. When the bonding process begins,an infrared (IR) camera may be used to perform the alignment. Silicon istransparent to IR light, so only the metal alignment keys will bevisible on the image. These metal alignment keys may then be manuallyaligned. In other embodiments, the alignment may be executedautomatically by an apparatus that includes the IR camera and an x-ymoveable stage.

FIGS. 8A-8B show a fabrication process according to another embodiment.In this embodiment, many of the process steps are performed after thejet plate 200 has been bonded to the component 100.

First, as described above, the metal alignment keys are created in thejet plate 200 and the component 100. In this embodiment, the metalalignment key 207 of the jet plate 200 is configured to appear withinthe metal alignment key of the component 100 when the parts are aligned.The metal alignment key is disposed in the top surface 201 of the jetplate 200 and the impingement surface 102 of the component 100.

Next, the jet plate 200 and the component 100 are planarized andthinned. As shown in FIG. 8A, the jet plate 200 may be thinned to athickness of about 500 μm, although other thicknesses may also be used.

The reservoir 210 is then etched into the top surface of the jet plate200. This etch process may be performed as described above with respectto FIG. 6B.

The component 100 and the jet plate 200 are then bonded together. Incertain embodiments, the impingement surface 102 of the component andthe top surface 201 of the jet plate 200 may be smoothed at this time,such as by a CMP process. This bonding may be performed using thetechnique described in FIG. 6F. The bonding of these two parts creates astack. Note that the outer surfaces of the stack have not yet beenprocessed. Rather, only the alignment keys and reservoir have beencreated.

FIG. 8B shows the subsequent processing of the jet plate 200 and thecomponent 100. First, the active surface of the component 100 may beprocessed. This processing may include implanting, metal deposition,etching and other traditional semiconductor fabrication processes.

The microjets 220 and exhaust ports 230 are then etched into the bottomsurface of the jet plate 200. This may be done in a manner similar tothat in FIG. 6D.

Finally, the active surface 101 may be further processed, such as byperforming pad lithography. Of course, in certain embodiments, theentirety of the active surface 101 may be processed before the bottomsurface 202 of the jet plate 200 is processed. In yet anotherembodiment, the bottom surface 202 of the jet plate 200 may be processedbefore the active surface 101 of the component 100.

In other words, there are various fabrication methods that may be used.In one embodiment, shown in FIGS. 6A-6F, each part (i.e. the jet plate200 and the component 100) is completely fabricated prior to beingbonded together. In another embodiment, shown in FIGS. 8A-8B, only thesurfaces of the jet plate 200 and the component 100 that are to bebonded are processed prior to bonding. All other processing is performedafter bonding is complete. In another embodiment, the internal surfacesare processed prior to bonding, as is performed in FIG. 8A. However, atleast one fabrication step is performed on the active surface 101 of thecomponent or the bottom surface 202 of the jet plate 200 prior to thebonding.

In all embodiments, when completed, the assembly comprises a component100, such as a semiconductor device, having a heat generating device,which is bonded on one surface to a jet plate 200. Further, both parts,the component 100 and the jet plate 200, can be fabricated using thesame semiconductor processes. This helps reduce size and weight.Integration may also improve the thermal performance of this thermalmanagement system as the thickness of the component 100 can be optimizedand built into the fabrication sequence.

In summary, unlike existing thermal management solutions, the jet plate200 with microjets 220 can be integrated directly into the component100, reducing the conductive resistance through the component 100. Thecombination of short conductive path to the impingement surface 102 andhigh convective heat transfer coefficients of the microjets 220significantly reduces the peak device temperature (at fixed duty cycleand power output) compared to existing thermal management solutions.Moreover, in single-phase embodiments, single-phase microjets 220provide convective heat transfer coefficients that meet or exceed thoseof multi-phase systems, but, unlike multi-phase systems, do not exhibitlimitations such as critical heat flux, dryout, or a need for exoticwettability coatings.

Additional enhancements may be made to the microjets described above.

FIG. 9 shows a cross-sectional view of a jet 260, as it passes through amicrojet 220 in the jet plate 200 and strikes an impingement surface102. Adjacent fluid, particularly if it is the same fluid, is entrainedinto the core of the jet 260 spreading the momentum of the jet 260 outto a larger and larger radius as the jet 260 propagates downstream. Atthe point where the centerline 261 of the jet 260 meets the impingementsurface 102, a stagnation point 262 exists due to symmetry. Near thisstagnation point 262, the flow turns from perpendicular to theimpingement surface 102 to parallel to the impingement surface 102. Theresulting parallel flow is often referred to as a wall jet 263. Further,the portion of the impingement surface 102 that is impinged in aperpendicular or substantially perpendicular direction is referred tothe impingement zone 108.

The average heat transfer coefficient and the surface area of theimpingement zone 108 dominate the heat transfer in microjetimplementations. Thus, in one embodiment, the surface area of theimpingement surface 102, and particularly the impingement zone 108, isincreased by creating structures on the impingement surface 102, asshown in FIG. 10. These area enhancement structures 107 may berectangular prisms, ranging in height. In one embodiment, the areaenhancement structures 107 are formed by etching the impingement surface102 of the component 100 prior to bonding the component 100 to the jetplate 200. In other embodiments, the area enhancement structures 107 maybe formed by depositing material on the impingement surface 102 prior tobonding. Of course, in other embodiments, the area enhancementstructures 107 may be different shapes.

As described above with respect to FIG. 9, the jet creates a wall jet263 as it travels parallel to the impingement surface 102. If an arrayof jets is used, such as is shown in FIG. 2, wall jets from eachmicrojet 220 will interact with its neighbors. This interaction createsa secondary stagnation point, which is equidistant from adjacentmicrojets 220. An array of microjets 220 may therefore exhibit degradedperformance due to these secondary stagnation points and cross-talkbetween neighboring microjets. FIG. 11 shows an array of microjets 220.As described above, at the center of each microjet 220, a primarystagnation point 270 is created. Further, at points equidistant fromadjacent microjets 220, secondary stagnation points 271 are created.

Some of the multifunctional features described herein not only mitigatethe cross-talk between neighboring microjets 220, but actually increasethe thermal performance of the overall array of microjets 220.

In one embodiment, the multifunctional features are implemented toincrease the overall heat transfer effectiveness by exploiting the heattransfer potential from the wall jets 263. For example, wall jetfeatures 300 may be constructed which are perpendicular to the flow ofthe wall jets 263, as shown in FIG. 12. When the wall jets 263 impingeon the wall jet features 300, an additional impingement zone is created,thus creating higher heat transfer coefficients at this locality. Thecreation of additional impingement zones, by exploiting the wall jets,increases the average heat transfer coefficient of the device.

The wall jet features 300 may vary in height. For example, the wall jetfeature 300 may extend from the jet plate 200 to the impingement surface102, as shown on the right side of FIG. 12. This is referred to as afull height feature. In this embodiment, the wall jet feature 300 may beformed on either the jet plate 200, or on the impingement surface 102 ofthe component 100. In another embodiment, the wall jet feature 300 mayextend only part of the way from the impingement surface 102 to the jetplate 200. This height may be acceptable, as the wall jet 263 does notexist at a significant velocity above the impingement surface 102. Forexample, the partial height wall jet features, shown as those shown inFIG. 13, may extend upward about 10 to 50 μm from the impingementsurface 102.

Wall jet features 300 differ from area enhancement structures 107 inseveral ways. First, the function of each is different. The areaenhancement structures 107 are intended to increase the surface area ofthe impingement zone 108. Thus, the exact shape of the area enhancementstructures 107 is not important; rather it is the fact that protrusionson the impingement surface 102 increase the surface area of theimpingement zone 108 that is important. In contrast, the wall jetfeatures 300 are designed to be perpendicular to the flow of the walljet 263. Secondly, these features are disposed in a different locationon the impingement surface 102. As seen in FIG. 10, the area enhancementstructures 107 are disposed in an impingement zone 108, which the jet260 strikes at a perpendicular or nearly perpendicular angle. Incontrast, the wall jet features 300 are positioned farther from themicrojets 220, where the flow of the jet 260 has become substantiallyparallel to the impingement surface 102. Stated differently, the areaenhancement structures 107 are typically disposed on the impingementsurface proximate the microjet 220 in the impingement zone 108. Incontrast, the wall jet features 300 are disposed farther away from themicrojets 220, outside of the impingement zone 108. The left side ofFIG. 12 shows an example of a wall jet feature 300, which is partialheight. These partial height wall jet features 300 would be incorporatedin the impingement surface 102 of the component 100.

Some multifunctional features may also be utilized to control ormanipulate the fluid flow characteristics. This flow control may helpavoid deleterious effects, such as cross-talk and wash-out typicallyobserved in large arrays. Specifically, the coolant that enters thearray via a microjet 220 must exit the reservoir 210. The flow of thisfluid away from the center of the array of microjets 220 may have adeleterious effect on the downstream stagnation area heat transfercoefficients.

Assume an array of microjets 220 configured as a 3×3 array. Coolant thatstrikes the impingement zone 108 below the center microjet 220 must exitthe reservoir 210 and reach the exhaust ports 230. The flow of thiseffluent may pass over the impingement zones 108 of the outer microjets220, thereby reducing the heat transfer coefficient at those regions.Thus, to counteract this effect of effluent flow, effluent flow controlfeatures may be incorporated into the jet plate 200 or the impingementsurface 102.

FIG. 14 shows a view of a jet plate 200 that includes an array ofmicrojets 220 and effluent flow control features 310. In thisembodiment, the effluent flow control features 310 are arranged todirect effluent from the center microjet 220 away from the impingementzones of the surrounding eight microjets 220. Thus, each of the eightsurrounding microjets 220 is configured with an effluent flow controlfeature 310 that is disposed between it and the center microjet 220.These effluent flow control features 310 force the effluent from thecenter microjet 220 to flow between the impingement zones of the outermicrojets 220. While FIG. 14 shows the effluent flow control featuresconfigured in one particular way, the disclosure is not limited to onlythis configuration. Any configuration where the effluent is routed dueto the presence of the effluent flow control features 310 may beemployed. In many embodiments, the effluent flow control features 310are used to route effluent from one microjet in such a way that it doesnot pass over the impingement zone of another microjet in the array.

In certain embodiments, the effluent flow control features 310 are fullheight. This term implies that the effluent flow control features 310occupy all of the vertical space between the impingement surface 102 andthe jet plate 200. In other words, this term implies that the feature isthe same height as the depth of the reservoir 210 (see FIG. 2).

Full height features can be fabricated in several ways. First, thesefull height features may be formed as an integral part of the jet plate200. In other words, when the jet plate 200 is etched to form thereservoir 210, photoresist or other masks are disposed over certainareas within the reservoir 210, so that these areas are not etched whenthe reservoir 210 is created. This would result in a full heightfeature. Alternatively, the full height features may be incorporated inthe component 100. This may be done through additive or subtractiveprocesses. In a third embodiment, part of the full height feature isformed on the impingement surface 102 of the component 100, while theremainder of the full height feature is formed on the jet plate 200.

Full height features may serve many purposes. For example, as describedalready, these features may serve as wall jet features 300 or effluentflow control features 310. However, full height features may serve otherfunctions as well. First, since these features extend across thereservoir 210, they can also serve as structural elements, furtherincreasing the integrity of the jet plate 200. As structural elements,the full height features serve to reinforce the jet plate 200 in thearea of the reservoir 210, potentially allowing thinner components 100,which may be advantageous thermally for minimizing resistance in thecomponent substrate.

Additionally, the full height features may also serve as alignmentfeatures during the bonding process. These full height features may alsobe used to control tolerancing of the device stackup as well.

Full height features may serve other functions, some of which are shownin FIG. 15. FIG. 15 shows wall jet features 300, which are partialheight, surrounding each of a plurality of microjets 220. Effluent flowcontrol features 310 are also shown, which are full height. FIG. 16shows a perspective view of several full height features, which may alsobe effluent flow control features 310. In certain embodiments, anelectrically conductive conduit 320 is created through one or more fullheight features, such as effluent flow control features 310. Theseelectrically conductive conduits 320 may be formed by etching a column340 (see FIG. 16) within the full height feature, and then filling thecolumn with an electrically conductive material, such as a metal. Theelectrically conductive conduit is exposed on the top surface of thefull height feature, such that when bonded to the component, is indirect contact with the impingement surface 102. The electricallyconductive conduit 320 may pass through the entirety of the jet plate200, and be accessible on the bottom surface 202 of the jet plate 200. Aconductive pad may be disposed on the impingement surface 102 of thecomponent 100, which aligns with the electrically conductive conduit 320when the jet plate 200 is bonded to the component 100. This allowscertain electrical signals to be accessible on the bottom surface 202 ofthe jet plate 200. In certain embodiments, the jet plate 200 may includeelectrical conduits so that an electrical signal from one full heightfeature may be routed to the electrical signal of a second full heightfeature, if desired.

Additionally, the full height features may also be fabricated so as toinclude a pathway 330 therethrough. This pathway 330 may be used as awaveguide for electromagnetic waves or light. Thus, the pathway 330 mayallow electromagnetic waves or light to travel from the bottom surface202 of the jet plate 200 to the impingement surface 102.

While FIGS. 15 and 16 show effluent flow control features 310, any fullheight feature may be used to serve any of these functions. As describedabove, these functions include wall jet features, effluent flow controlfeatures, structural elements, alignment mechanisms, electricallyconductive conduits, or waveguides. In certain embodiments, a fullheight feature may perform two or more of these functions.

The jet plate 200 is intended for use in single-phase systems. However,it is understood that the enhancements to the jet plate 200 and theimpingement surface may apply to both single-phase and multi-phasesystems. For example, the wall jet features, and effluent flow controlfeatures may be applied to both single-phase and multi-phase systems.

In one embodiment, the present disclosure discloses a method of coolinga semiconductor component. First, one side of the jet plate 200 isattached, adhered or otherwise connected to the semiconductor component.In certain embodiments, the jet plate 200 is attached to the side of thesemiconductor component opposite the heat generating device 110. Asource of pressurized coolant fluid is then connected to the oppositeside of the jet plate 200. A sink or return for exhausted fluid is thenattached to the exhaust ports of the jet plate 200. A coolant fluid isthen introduced through the microjet array. Importantly, this is asingle-phase coolant fluid, meaning that it does not change phase (i.e.boil). The coolant fluid strikes the impingement surface of thesemiconductor component and is then exhausted through the exhaust portinto the sink. In certain embodiments, the heat transfer properties areimproved by increasing the surface area of the impingement surface. Incertain embodiments, the heat transfer properties are improved byproviding wall jet features, which extend perpendicular to theimpingement surface. These wall jet features are impacted by the jetwall as it moves away from the impingement surface. In certainembodiments, the heat transfer properties are increased by routing theeffluent toward the exhaust ports. The effluent flow control featuresmay route the effluent so that it avoids the impingement surfaces ofadjacent microjets in the array. In certain embodiments, thesingle-phase coolant fluid strikes the surface of the semiconductorcomponent. In other embodiments, a conductive ground plane may bedisposed on the side of the semiconductor component opposite the heatgenerating device. In these embodiments, the single-phase coolant fluidstrikes the ground plane.

In certain embodiments, the jet plate 200 may be attached to the side ofthe semiconductor component where the heat generating device isdisposed. In these embodiments, the coolant fluid must be electricallynon-conductive. For example, air may be used as the coolant fluid inthis embodiment.

The present disclosure is not to be limited in scope by the specificembodiments described herein. Indeed, other various embodiments of andmodifications to the present disclosure, in addition to those describedherein, will be apparent to those of ordinary skill in the art from theforegoing description and accompanying drawings. Thus, such otherembodiments and modifications are intended to fall within the scope ofthe present disclosure. Furthermore, although the present disclosure hasbeen described herein in the context of a particular implementation in aparticular environment for a particular purpose, those of ordinary skillin the art will recognize that its usefulness is not limited thereto andthat the present disclosure may be beneficially implemented in anynumber of environments for any number of purposes. Accordingly, theclaims set forth below should be construed in view of the full breadthand spirit of the present disclosure as described herein.

What is claimed is:
 1. An assembly, comprising: a semiconductorcomponent, disposed on a semiconductor substrate, and having a heatgenerating device disposed therein, wherein one surface of thesemiconductor substrate that is configured to be directly contacted by afluid is referred to as an impingement surface; a jet plate, where areservoir is formed within the assembly as a sealed enclosure bounded bythe jet plate and the impingement surface, the jet plate comprises aplurality of microjets arranged as a two-dimensional array and at leastone exhaust port, and each of the microjets and the exhaust port are incommunication with the reservoir; a region of the impingement surfacewhere a flow of the fluid from each of the plurality of microjets isperpendicular to the impingement surface is defined as an impingementzone; and at least one feature, disposed in the reservoir, each featureextending from the jet plate to the impingement surface, configured toserve as a structural member and disposed outside each of theimpingement zones, wherein the at least one feature comprises a wall jetfeature and/or an effluent flow control feature.
 2. The assembly ofclaim 1, wherein a smallest perimeter that surrounds the two-dimensionalarray does not include the at least one exhaust port.
 3. The assembly ofclaim 1, wherein the fluid is single-phase.
 4. The assembly of claim 1,wherein the at least one feature increases heat transfer between thefluid and the impingement surface.
 5. The assembly of claim 4, whereinthe at least one feature increases the heat transfer between the fluidand the impingement surface by way of increased contact area.
 6. Theassembly of claim 4, wherein the at least one feature increases the heattransfer between the fluid and the impingement surface by way ofenhanced momentum transfer via a secondary impingement zone.
 7. Theassembly of claim 1, wherein the at least one feature extends into thereservoir and contacts the impingement surface and the jet plate.
 8. Theassembly of claim 7, wherein a channel is disposed within the at leastone feature.
 9. The assembly of claim 8, wherein the channel comprisesan electrical conduit.
 10. The assembly of claim 8, wherein the channelcomprises a pathway allowing light and electromagnetic waves to passtherethrough.
 11. The assembly of claim 1, wherein the at least onefeature serves as an alignment feature.